Single lamp illumination system for a dual plane flat-bed scanner

ABSTRACT

A scanning apparatus providing separate fixed object focal planes for transmissive and reflective original documents to be scanned, wherein a scan carriage containing illumination, sensor, and optical elements is moved together to scan an original document and to obtain a digitized representation thereof. The movable scan carriage has an illumination source disposed between the reflective and transmissive object focal planes, with the object focal plane to be used selected by changing the position of a single optical element within the scan carriage. The illumination source comprises a single lamp disposed for correct illumination of the selected object focal plane. Automatic resolution selection and focusing of the original image can occur using a converging device comprising a first and second focusing lens.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.08/496,511, filed Jun. 29, 1995 now U.S. Pat. No. 5,696,609, entitled"ILLUMINATION SYSTEM FOR A FLAT-BED SCANNING SYSTEM."

This application is related to application Ser. No. 08/922,968, entitled"TWO LENS CONVERGING DEVICE IN A DUAL PLANE FLAT-BED SCANNING SYSTEM"(Attorney Docket No, XP-0510) which is filed simultaneously with thefiling of this application, the disclosure of which is incorporated byreference.

BACKGROUND

The field of the present invention is optical scanning ofhigh-resolution color images, and in particular, the use of a flat-bedscanner system for the scanning of reflective and transmissive originaldocuments at high resolution in a high volume production environmenttypical in the graphic arts electronic prepress industry. The originaldocuments scanned by such systems include color or monochromephotographs, artwork, and composed pages of text and graphics. Theactual graphic image content of the scanned original document isreferred to as an "original".

In use of a flat-bed scanner for reflective scanning, an original on anopaque substrate is placed with the surface containing the originalfacing down on a flat transparent reference surface, typically glass.The original document is fixed on the surface such that a single line ofthe original, herein after referred to as a "scan line" is illuminatedfrom below, and the light reflected from the scan line is directedthrough an optical system to form an image of the scan line on a sensorsuch as a CCD array, which converts the optical signal to an electronicrepresentation of the scan line, comprising a line of digital pictureelements, or "pixels". The desired portion of the original is scanned,one scan line at a time, by moving the original relative to theillumination system, optical system, and sensor along a directionhereinafter referred to as the "scanning axis". In systems typical ofthe prior art, such as that disclosed in U.S. Pat. No. 5,341,225, theillumination system, optical system and sensor are configured to movetogether as a unit. In other systems, such as those of U.S. Pat. No.5,140,443, the original is moved while the illumination system, opticalsystem and sensor remain fixed. In a production environment, originaldocuments are scanned in a sequence, with each requiring a preparationstep in which the original to be scanned is located and fixed on thesurface in proper alignment and registration, followed by the actualscanning operation.

A transparent original document, typically a photographic transparency,comprises an original on one side of a thin transparent substrate. Inthis case, the original is illuminated from the side opposite from thatcontaining the optical system and sensor. Use of a single flat-bedscanner for both types of scanning involves a modal configurationchange. Typically, a flipcover used in reflective scanning mode to holdthe original document flat on the transparent surface is replaced by atransmissive illumination module which illuminates from above theportion of the original to be scanned. As in reflective-mode scanning,prior art systems are configured so that either the original or one ormore scanner illumination, optics or sensor components move to carry outthe scanning process.

In addition to reconfiguration of the illumination system, themagnification of the optical system is typically changed so that thesame number of pixels imaged on the CCD array, and captured by thedigitizing electronics, corresponds to a larger or smaller area of theoriginal. In high-resolution scanning systems typically in use ingraphic arts electronic prepress processing, transparencies areoftentimes scanned at resolutions of 2,000 to 4000 pixels per inch (ppi)or greater, while reflective originals are usually scanned at much lowerresolutions, for example 600 to 800 ppi. Accordingly, in a productionenvironment in which both reflective and transmissive originals are tobe scanned in a mixed processing sequence, mode changes involvingillumination system and resolution settings can add significantly to thetime required for job processing.

Accordingly, it is an object of the present invention to provide a lowcost apparatus for color scanning both reflective and transmissiveoriginal documents.

It is another object of the present invention to provide a scanningapparatus with increased scanning efficiency.

It is a further object of the present invention that a singleillumination source be used for illuminating both reflective andtransmissive original documents.

It is still another object of the present invention to minimize thenumber of folds in the optical pathway.

It is yet another object of the present invention to provide a scanningapparatus for scanning transmissive original documents at low and highresolution.

Additional objects, advantages, novel features of the present inventionwill become apparent to those skilled in the art from this disclosure,including the following detailed description, as well as by practice ofthe invention. While the invention is described below with reference topreferred embodiment(s), it should be understood that the invention isnot limited thereto. Those of ordinary skill in the art having access tothe teachings herein will recognize additional implementations,modifications, and embodiments, as well as other fields of use, whichare within the scope of the invention as disclosed and claimed hereinand with respect to which the invention could be of significant utility.

SUMMARY OF THE INVENTION

The apparatus comprises a flat-bed scanner providing separate fixedobject focal planes for transmissive and reflective originals, wherein amovable module, hereinafter referred to as a "scan carriage", containingillumination, sensor, and optical elements is moved to scan an original.The movable scan carriage has an illumination source disposed betweenthe two object focal planes, with the object focal plane to be used(transmissive or reflective) selected by changing the position of one ormore optical elements within the scan carriage. The magnification of theoptical system, i.e., the resolution of the digital representation ofthe original, can be adjusted independently of the selection of anobject focal plane. A converging device is provided within the scancarriage for adjusting the resolution of the original image, singly orin combination with the motion of another mirror. The converging deviceincludes at least a first and second optical lens mounted on a lenscarriage and a drive device for moving either lens into an opticalpathway containing an original image. The drive device may also be usedto move the optical lenses closer to or further from an image sensor forautomatically focusing the original image onto the image sensor.

The positioning of optical elements to select the object focal plane isthe subject of several embodiments to be described in detail below. Oneor more mirrors can be moved so as to retain the total optical pathlength between the selected object focal plane and the sensor focalplane, i.e., the plane on which the original is imaged on the sensor.

The illumination system can be configured according to the object focalplane selected, using an elongated lamp disposed along an axissubstantially parallel to the scan line axis of an original at theselected object focal plane. In the preferred embodiment, the singletubular lamp is disposed in the movable scan carriage such that the lampis used to illuminate a scan line in both the reflective andtransmissive modes using additional optical components, such as a switchmirror, to direct light to the directed object focal plane.

The transmissive object focal plane is fixed with respect to thescanning apparatus, located between the illumination system and theother optical components. In one embodiment, a removable transparencyholder is used for access to the transmissive object focal plane, andfor accurate placement of an original document to be scanned beforeinsertion into the scanner. In alternate embodiments, the action ofinsertion or removal of the transparency holder is used, throughappropriate linkages with illumination system elements and/or opticalelements, to select the transmissive or reflective focal planesrespectively.

The scan carriage is moved along a scanning axis from one end of theoriginal to be scanned to the other, carrying the illumination, opticsand sensor systems within it.

The use of a single switch mirror in combination with the resolutionselection of the original image enables three distinct scanningmodes: 1) reflective mode, low-resolution, 2) transmissive mode,low-resolution, and 3) transmissive mode, high-resolution. The opticalpath length of the first two configurations are the same while the pathlength for the third configuration is shorter which enables the higherresolution capability.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will best beunderstood from a detailed description of a preferred embodiment thereofselected for the purposes of illustration and shown in the accompanyingdrawings, in which:

FIG. 1A and FIG. 1B show perspective views of a single object focalplane dual-mode flat-bed scanner, configured according to the prior artfor reflective and transmissive original scanning, respectively.

FIG. 2A and FIG. 2B show in block diagram form a dual object focal planescanning apparatus according to the present invention, providingreflective and transmissive scanning modes, respectively;

FIG. 3A and FIG. 3B illustrate the selection of object focal planes bymotion of a single mirror in the moving scan carriage;

FIG. 4A and FIG. 4B illustrate the selection of object focal planes bymotion of a mirror pair in the moving scan carriage;

FIG. 5A and FIG. 5B show an alternate embodiment with a single movablemirror for object focal plane selection;

FIG. 6A illustrates resolution selection by linear motion of a fixedfocal-length lens;

FIG. 6B illustrates resolution selection by changing the focal length ofa zoom lens;

FIG. 7A and FIG. 7B illustrate resolution selection by rotating a lensabout an axis perpendicular to its optic axis;

FIG. 7C illustrates resolution selection by multiple rotations of a lensabout an axis perpendicular to its optic axis;

FIG. 8 shows an embodiment comprising an optical path folded in threedimensions;

FIG. 9A and FIG. 9B show a dual-mode scanner illumination configurationwith a single lamp according to the invention;

FIG. 10A and FIG. 10B show illumination configurations employing arotating lamp element;

FIG. 11A and FIG. 11B show two-lamp illumination configurationsemploying diffusers;

FIG. 12A, FIG. 12B and FIG. 12C show two-lamp illuminationconfigurations employing removably-disposed diffusers, reflectors, ordiffuser reflector combinations;

FIG. 13A and FIG. 13B show three-lamp illumination configurations;

FIG. 14A and FIG. 14B show top and side views of a removable lampcartridge with three lamps;

FIG. 15A, FIG. 15B and FIG. 15C illustrate use of a removabletransmissive original holder for selection of illumination mode;

FIG. 16A, FIG. 16B and FIG. 16C illustrate use of a removabletransmissive original holder for positioning optical elements forselection of an object focal plane;

FIG. 17A and FIG. 17B illustrate the use of a dark slide for dustprotection and dark current calibration;

FIG. 18A, FIG. 18B and FIG. 18C illustrate the use of an apertureshutter/dark slide combination for dust protection, dark currentcalibration, and reduction of the effects of flare within the movingcarriage;

FIG. 19A and FIG. 19B show top and side views of a linear drive systemfor a scanner carriage, using helically-wound bands;

FIG. 20A and FIG. 20B show top and side views of a drive system whereinthe scan line axis of an scanned original passes through a center ofrotation of the scanning module;

FIG. 21 illustrates an embodiment wherein position encoding utilizeselements of a CCD array;

FIG. 22A and FIG. 22B show top and side views of an alignment gridsystem for reflective originals according to the invention;

FIG. 23 illustrates the scanning of a reflective original document heldin the Rx object focal plane at low-resolution;

FIG. 24 illustrates an embodiment of the present invention wherein asecond mirror is used to illuminate the reflective original documentheld in the Rx object focal plane;

FIG. 25A and FIG. 25B illustrate the positioning of the switch mirrorshown in FIG. 23;

FIG. 26 illustrates the rotation of the switch mirror shown in FIG. 23by insertion of a transmissive slide holder for scanning transmissiveoriginal documents;

FIG. 27 illustrates the scanning of a transmissive original documentheld in the Tx object focal plane at low resolution;

FIG. 28 further details the switch mirror shown in FIG. 27;

FIG. 29 illustrates the scanning of a transmissive original held in theTx object focal plane at high resolution;

FIG. 30 illustrates an embodiment of the present invention for scanningoriginal documents in either reflective or transmissive object focalplane;

FIG. 31A and FIG. 31B illustrate the selection of a low or highresolution lens; and

FIG. 31C further details the lens carriage shown in FIG. 31A and FIG.31B.

DETAILED DESCRIPTION OF INVENTION

Turning now to the drawings, the various embodiments of the inventionwill be described with respect to the optical system, illuminationsystem, linear drive system, and other components, wherein likereference numerals refer to like elements throughout the drawings. FIG.1A and FIG. 1B show perspective views of a dual mode flat-bed scanneraccording to the prior art. In FIG. 1A, a scanner 100 is configured forthe reflective scanning mode. An original document 102 is placed withthe surface 104 containing the original 103 to be scanned facing down ona transparent surface 106, and held in place by a flipcover 108. Thesurface is illuminated from below by lamps 110, producing a scan line113 having a scan line axis 114, wherein the lamps 110 are disposedsubstantially parallel to the scan line axis 114. The scanning opticsand sensor electronics are located in scan module 112, which is driventogether with lamps 110 such as to move the scan line 113 from one end116 of the original document 102 to the other end 110 of originaldocument 102.

In FIG. 1B, the same scanner 100 is re-configured for the transmissivescanning mode. Flipcover 108 is replaced by a transmissive illuminationmodule 120 which can be raised to position 122 for insertion or removalof a transparent original document 124 to be scanned. An illuminationsystem, shown in the drawing as lamp 126, is disposed so as toilluminate scan line 113 of the transparent original document 124 fromabove along scan line axis 124, thereby allowing scanning of theilluminated transparent original document 124 by the scan module 112.

FIG. 2A and FIG. 2B show block diagram views of a dual mode flat-bedscanning apparatus according to the invention. In FIG. 2A, a reflectiveoriginal document 102 is placed with the original 103 to be scanned onthe surface 106, hereinafter referred to as the "Rx object focal plane".A second object focal plane 210 is located below the Rx object focalplane 106 and hereinafter referred to as the "Tx object focal plane", tobe described further below. The scan carriage 220 comprises illuminationsystem 222, optical system 224 and sensing system 226. The illuminationsystem 222 includes one or more lamps and other components (not shown),disposed so as to illuminate the original 103 along scan line 113. Ofcourse, as should be readily apparent, scan line 113 extendsperpendicularly out of the page along scan axis 114 (not shown).

The optical system 224 includes one or more focusing elements, (assumedin this discussion to be a focusing lens 228) possibly combined withother optical components to determine an optical path 229, having opticaxis 230, from scan line 113 to sensor focal plane 232. The sensingsystem 226 comprises a linear sensor array 234 together with electronicsused for data acquisition and control (not shown). For the purposes ofthis discussion, it is assumed that the array 234 is a linear CCD array,but alternate sensor systems can be used as well.

A linear drive system 236 is used to move the scan carriage 220 and thecomponents fixed within it along a scanning axis 238 from its startingposition 239 to end of scan position 240, with optic axis 230 moved toposition 242, thereby scanning the original 103, which remains fixed ina stationary position on the Rx object focal plane 106.

In FIG. 2B, the apparatus of FIG. 2A has been reconfigured fortransparency scanning mode. A transparent original document 124 isplaced with its emulsion surface in the Tx object focal plane 210.Illumination system 222 illuminates the scan line 113 in Tx object focalplane 210, and optical system 224 is changed such as to focus the scanline 113 at sensor focal plane 232. As in reflective scan mode, theoriginal document 124 remains stationary as the scan carriage 220 isdriven along scanning axis 238 by linear drive system 236 from beginningof scan to end of scan.

Optical System

The optical system of the scan carriage 220 provides three functions:(1) selection of the object focal plane as described above; (2)determination of the magnification of the object projected upon thesensor focal plane 232; and, (3) folding of the optical path 229 forefficient use of the physical volume within the scan carriage 220. Thesefunctions will be considered in the discussion and drawings to follow.

FIG. 3A and FIG. 3B illustrate the use of a single mirror for selectionbetween the Rx and Tx object focal planes for reflective andtransmissive originals, respectively. In FIG. 3A, a lens 310 focuses ascan line 312 in the Rx object focal plane 314 on a sensor array 316using two fixed mirrors 318 and one movable mirror 320 to fold theoptical path accordingly. In FIG. 3B, the mirror 320 has been moved alinear distance D to position 322, where the distance D is theseparation distance between the Rx object focal plane 314 and the Txobject focal plane 324. The total optical path length from scan line 312to sensor focal plane 316 therefore remains constant.

FIG. 4A and FIG. 4B illustrate the use of a movable pair of mirrors forselection between the Rx and Tx object focal planes. In FIG. 4A, fixedmirror 410 is used together with movable mirror pair 412 to select Rxobject focal plane 314. In FIG. 4B, the movable mirror pair 412 has beenmoved a linear distance D/2 to position 414, where D is again theseparation distance between Rx object focal plane 314 and Tx objectfocal plane 324.

In the configurations of FIG. 3A through FIG. 4B described above, aconstant optical path between the selected object focal plane is foldedsubstantially horizontally, using the vertically disposed fixed mirrorpair 318 in FIG. 3A and vertically disposed movable mirror pair 412 inFIG. 4A. A consequence of these configurations is that the first mirrorin each case (mirror 320 in FIG. 3A and mirror 410 in FIG. 4A) is closeto the selected object focal plane, causing potential degradation of thedigitized image as a result of dust settling on the mirror surface. Thisdegradation is due to the fact that, for long focal length lensestypically used in scanning systems, dust particles close to the objectfocal plane can be partially focused at the sensor focal plane, and cantherefore cause digitized image contamination for originals at thenearest object focal plane, i.e., at the Tx object focal plane 324. Thiscan be seen from the fact that the peak-to-peak signal variation V alongthe sensor focal plane as a result of dust having a mean radius a on asurface located a distance d from the object focal plane is given by:##EQU1##

where NA is the working numerical aperture of the object space. As arule of thumb, d should be great enough so that V≦˜20% if uncorrectabledegradation of the digitized image is to be avoided.

There exist variations on the configurations of FIG. 3A through FIG. 4Bin which the first mirror is kept at maximum distance, for example byfolding the beam over itself (interchanging the positions of mirror 320and lens 310 in FIG. 3A). Such configurations usually require morephysical volume, however, in order to avoid "collisions" between theoptical components (e.g., between mirror 322 and lens 310 in FIG. 3B).

FIG. 5A and FIG. 5B show an embodiment wherein a single mirror is movedto select between alternate optical paths of the same total path length,using a fixed pair of mirrors disposed horizontally so as to fold thebeam vertically. In FIG. 5A, the scan line 312 is focused by lens 310 onsensor array 316 using fixed mirror pair 510 and movable mirror 512. InFIG. 5B, the mirror 512 has been moved a linear distance D to position514, where D is the separation distance between the Rx object focalplane 314 and the Tx object focal plane 324. In this case moving themirror 512 has the effect of reversing the folding direction, andfolding the beam back over itself.

This configuration has the immediate advantage that the first reflectingmirror in each case is one of the mirror pair 510, which can be placedfar enough from the nearest object focal plane (the Tx object focalplane 324 in this case) to minimize variations due to dust as given byequation [1] and the components are readily configured to avoid"collisions" of the type described above. The fact that the two mirrorsof the pair 510 have upward facing faces 516 and 518 makes them moresusceptible to dust settling, but since according to equation [1] thedust is not focused at the sensor array 316, its presence has only theeffect of uniformly diminishing the image intensity. Protection againstdust by sealing the scan carriage (to be discussed further later in thisspecification) is a way of minimizing this effect.

The resolution of a digitized image obtained by scanning is determinedby the number of resolution elements at the sensor plane and themagnification of the optical system. For the case of a linear CCD sensorarray, the resolution r is determined by: ##EQU2##

where a is a measure of the CCD element density (e.g., elements perinch), S_(O) and S_(S) are the effective optical path distances of theobject and sensor to the focusing lens, respectively. Accordingly, theresolutions available in a CCD scanner are determined by changing theoptical path distances S_(O) and S_(S), by moving one or more elementsof the optical system, as described and illustrated in the followingfigures.

FIG. 6A illustrates resolution selection by moving a fixed focal lengthlens, using the optical configuration of FIG. 5A as a reference. In thedrawing, lens 610 having fixed focal length F is moved a distance L toposition 612. The condition for the object at scan line 312 for the Rxobject focal plane 314 to be focused at sensor plane 316 is given by thefollowing well-known equation:

    1/S.sub.O =1/F-1/S.sub.S                                   [ 3]

As a result, one or more elements of the optical system have to move inaddition to the lens 610 to satisfy the condition [3]. In the drawing,the sensor plane 316 is fixed and mirror pair 510 is moved a distance Mto position 614, thereby adjusting the distance S_(O) as required. In analternative arrangement, the position of the sensor array 316 can bemoved instead of or in addition to the mirror pair 510.

In FIG. 6B, a compound lens with variable focal length is used as thefocusing lens. In this case, moving the lens 620 a distance Z toposition 622 while at the same time changing its focal length can selecta new magnification while ensuring satisfaction of equation [3].

Although image resolutions can be continuously variable over a range ofvalues, they are usually selected from a fixed set specified for thescanner system, using mechanical linkages which permit continuousmovement of the focusing lens or its elements and other optical elementsas necessary to satisfy equation [3] at all times. The followingdiscussion is directed to means for changing the position of a focusinglens in discrete steps corresponding to selected resolutions.

FIG. 7A and FIG. 7B illustrate an alternative to direct linear motion ofa lens for positioning, wherein a lens is rotated about an axissubstantially perpendicular to its optic axis. A lens 710 having anoptic axis 706 is mounted in an assembly 712 configured for rotationthrough an angle substantially equal to 180° thereby moving lens 710 toa new position 714. Shafts 716 and 718 coaxial with axis of rotation 720are constrained by bearings 722 and 724. The effective center 726 oflens 710 is offset from axis of rotation 720 by a distance L/2, where Lis the distance between the original lens position 726 and the new lensposition 728.

FIG. 7C illustrates a variation of the above configuration, in which alens assembly 730 contains a lens 732 with side shafts 734 and 736arranged such that a succession of "tumbling" operations (738, 740 and742 for example) bring the lens 732 into a new registered position alonga guide 744 having indentations 746 to receive and position side shafts734 and 736. Each such "tumble" of the assembly moves the lens center adistance T along guide 744 in a direction substantially parallel to theoptic axis 748 of lens 732.

From the previous discussions it is clear that in the apparatus of theinvention the selection of object focal plane can be accomplishedindependently of resolution selection. In most cases, however, adifferent set of resolutions are selected for transparencies than forreflective original documents. Accordingly, switching from reflective totransmissive mode typically combines object focal plane and resolutionselection operations. Returning to one mode after having selected theother restores the operational parameters, including resolution,applicable to that mode, thereby allowing intermixing of transparencieswith reflective original documents in a processing sequence with aminimum of reconfiguration operations, in accordance with the objectivesof the invention.

Since illumination, optical imaging, and sensing systems are allcontained in the movable scan carriage, it is desirable to arrange thesecomponents to use the physical volume as efficiently as possible inorder to avoid excessive size and mass of the movable carriage. It iswell known in the art that folding the beam is one means for reducingthe volume occupied by the optical path. Traditional scanning systemsfold the beam in a single plane, as is illustrated in the configurationsof FIG. 3A through FIG. 6B. As has been indicated, one of thelimitations imposed upon beam folding configurations is "collisions" ofcomponents when they are moved for object focal plane and/or resolutionselection.

One solution to the volume-efficiency problem lies in folding the beamin three dimensions, as illustrated in FIG. 8, which is a perspectiveview of an optics and sensor subassembly for an embodiment of theinvention. An original 810 in object focal plane 812 is scanned one scanline 814 at a time by moving a scan carriage (not shown) containingsubassembly 816 along scanning axis 818 in direction 820. Focusing lens822 is used with a movable mirror pair 824 and a fixed mirror 826 toimage scan line 814 on CCD array 828 mounted perpendicular to and in aplane substantially parallel to scanning axis 818. Mirror pair 824 canbe moved through focal adjustment range 830 (to the lowest position at832) to select the object focal plane and to compensate for movements834 of lens 822 for resolution adjustments. The use of the fixed mirror826 to fold the optical path 836 in a third dimension has the effect ofshortening the dimension of the scan carriage sub-assembly 816 in thedirection parallel to the scanning axis 818 at the expense of additionalwidth in the direction parallel to the axis of lens 822. The ranges ofmovements 830 and 834, for movement of the mirror pair 824 and lens 822respectively, are determined by the physical dimensions of theenclosure, the optical path and lens parameters, and position of mirror826.

Illumination System

The various embodiments of illumination system 222 of FIG. 2A aredescribed in the discussion and drawings to follow. One or more tubularlamps of the fluorescent type (warm cathode or cold cathode) aredisposed parallel to the scan line so as to illuminate it at the objectfocal plane determined by the scanning mode (reflective or transmissive)in use. The line of illumination incident at the scan line at the objectfocal plane is referred to herein as the "illumination axis". In typicalscanner illumination configurations, a pair of lamps are disposed so asto provide simultaneous illumination from both sides of a reflectivemode illumination axis and directed upward to the scan line. Fortransmissive originals, only a single lamp is generally required,providing illumination of an object point from above the object focalplane and substantially coincident with a transmissive mode illuminationaxis. Since the transparent substrate of a transmissive originaldocument is subject to surface scratches which can be imaged at thesensor plane if illuminated by a directed beam of light, means such asreflectors and/or diffusers are used to provide illumination within anacute angle from the illumination axis so as to minimize this effect.

Configurations of one, two and three lamps are illustrated in thedrawings of FIG. 9A through FIG. 13B FIG. 9A and FIG. 9B show examplesof illumination using a single lamp for reflective and transmissivescanning modes respectively. In FIG. 9A, a single lamp 910 providesdirect side illumination of scan line 113 (perpendicular to page) andindirect side illumination through a fixed focusing mirror 912. The Rxobject focal plane 106 is the top surface of a transparent layer 914(e.g. glass), holding the reflective original document 102 beingscanned. A reflective lamp collar 916 is rotatably disposed about theaxis 918 of lamp 910 such as to direct the illumination through anelongated opening 911 containing the direct and indirect illuminationpaths. The scan line axis 114 (not shown) of scan line 113 issubstantially coincident with the illumination axis 920 (perpendicularto page) for the reflective scanning mode.

In FIG. 9B, reflective collar 916 has been rotated about axis 918 so asto illuminate a transparency 124 held at the Tx object focal plane 210along a scan line 113 substantially perpendicular to optic axis 230. Apair of reflectors 922 reflects the illumination from lamp 910 so as toprovide for scratch suppression as described above. In this example,changing modes is accomplished by rotating reflective collar 916 toshift the reflective mode illumination axis 920 to the transmissive modeillumination axis 924 (perpendicular to page), together with motion ofthe illumination system 222 relative to the optical system 224 such asto shift the scan line 113 accordingly.

In the example of FIG. 9A and FIG. 9B, as well as others to follow, arotating reflective collar 916 has been used to redirect the light forillumination mode change. Other embodiments can be used to achievesimilar results. For example, an alternative to rotating reflectivecollar 916 rotating about fixed (clear) lamp 910 is a rotatably-disposedlamp having an elongated aperture parallel to lamp axis 910, and havinga (light-sealed) reflecting interior surface everywhere else. A secondalternative comprises the use of a fixed lamp having two elongatedapertures parallel to lamp axis 918 together with a rotating reflectivecollar 916 which selects the aperture appropriate for the illuminationmode. Although the reflective collar is shown for the sake of simplicityin the following examples, it will be clear to one skilled in the artthat alternatives including those described above can be used as well.

FIG. 10A and FIG. 10B show comparable embodiments using two parallellamps instead of a single lamp and mirror. Both lamps 910 and 1010 areused for reflective mode scanning as shown in FIG. 10A, whereas onlylamp 910 is used for transmissive mode scanning as shown in FIG. 10B.Again, mode change is accomplished by rotation of the reflective collar916 and relative motion of the illumination system 222. In thisconfiguration, as in those of FIG. 9A and FIG. 9B, a document 102 onreflective scanning surface 924 has no effect upon scanning intransmissive scanning mode.

FIG. 11A and FIG. 11B illustrate the use of a substantially flatdiffuser to redirect the light of a fixed pair of lamps when intransmissive scanning mode. In FIG. 11A, the lamps 910 and 1010illuminate scan line 113 at illumination axis 920 in Rx object focalplane 106 as in the previous example. Mode change from reflectivescanning mode to transmissive scanning mode is accompanied by use of adiffuser as shown in FIG. 11B. In the simplest case, document 102 isreplaced by a high-efficiency diffusing reflector 1110, comprising asheet of translucent material with a reflective back surface 1116,thereby directing the light down to scan line 113 in Tx plane 210.Although no motion of the illumination system 222 takes place relativeto optical system 224 of FIG. 2A, extra work steps are involved inreplacing the document 102 with the diffuser sheet 1110. An alternativeis the use of a removably disposed diffuser reflector sheet 1112 betweenthe transparent layer 914 and the lamps 910 and 1010. In this case, amode change is accompanied by insertion or removal 1114 of the diffuserreflector sheet 1112, without the necessity of replacing a document 102lying on reflective scanning surface 106.

FIG. 12A through FIG. 12C show embodiments which elaborate on those ofFIG. 11B, wherein diffusing and/or reflecting elements are inserted orwithdrawn between the lamps and the reflective scanning surface toaccompany a scanning mode change. In FIG. 12A, a diffuser reflectormodule 1210 having a back reflecting surface 1212 redirects the lightfrom lamps 910 and 1010 to scan line 113 in Tx object focal plane 210.Motion 1114 of the module 1210 is used to switch modes.

FIG. 12B and FIG. 12C show variations of that described above. In FIG.12B, a module 1214 is used, having a front reflecting surface 1216,thereby providing specularly-reflected (e.g., focused) instead of purelydiffuse illumination as in the previous examples. Again, motion 124 ofthe module 1214 is used to switch modes. In FIG. 12C, a single fixedlamp 1010 is used with a rotating mirror 1218 to direct illumination toscan line 113 in Tx object focal plane 210. In this embodiment, arotation 1220 of mirror 1218 is used to change between transmissive andreflective scanning modes. In each of the embodiments illustrated inFIGS. 12A-12C, a mode change from transmissive to reflective scanningshifts the illumination axis from the transmissive mode illuminationaxis 924 to the reflective mode illumination axis 920 (and vice-versa).

FIG. 13A and FIG. 13B show two configurations of three lamps, with twodedicated to reflective scanning and one to transmissive scanning. Theseconfigurations have the advantage that lamps associated with eachscanning mode wear uniformly without requiring lamps dedicated to themode not in use to be lit. In FIG. 13A, lamps 910 and 1010 are used forreflective scanning, and lamp 1310 for transmissive scanning. Since theillumination axes of the lamp systems are not coincident, theillumination system 222 is moved relative to the optical system 224, asin examples of FIG. 9A through FIG. 10B discussed above. In thisexample, the transmissive mode lamp 1310 is disposed using reflectingcollar 1312 to direct diffuse illumination downward, using reflectors922 for scratch suppression as discussed previously.

In FIG. 13B, an alternative configuration is shown, wherein thetransmissive mode lamp 1310 is disposed with reflecting collar 1312 soas to direct illumination other than downward, e.g., substantiallyhorizontally as shown in the drawing, using a reflecting mirror 1316 toredirect the light toward the Tx object focal plane 210. Thisconfiguration eliminates localized variations in illumination along thelamp due to settling of particulate matter along its lower insidesurface 1314 as the lamp ages. It is to be noted that alternativeconfigurations of mirrors and/or lenses can also be used for theredirection of light.

FIG. 14A and FIG. 14B show top and side views of an embodiment of anillumination system comprising three dedicated lamps fixed within aremovable lamp module. This configuration has the advantage of ease ofreplacement, automatic alignment of the illumination components, anduniformity of wear as described above.

The drawings show a scanner 100 with movable scan carriage 220positioned for module interchange. For the purposes of this discussion,one of the two extreme limits 1424 of carriage travel, hereinafterreferred to as the "scan carriage home position", is assumed. Removablemodule 1410 is disposed within scan carriage 220 for precise positioningof the three lamps 1412, 1414 and 1416. Access to module 1410 isprovided by an opening in the scanner case having a flip-down cover1422, allowing insertion or removal of the module (shown by arrow 1426).Keyed electrical contacts 1428 assure proper registration of the lampsand power connections for their operation.

Prepositioning of the lamps 1412, 1414, and 1416 in manufacture of themodule 1410 assures accuracy of optical alignment and minimumcontamination due to handling. Openings and surfaces are designed formaximum capture of light with minimum accompanying flare from unwantedreflected light, using reflective surfaces 1430 and 1432 for directionof light, and absorptive surface 1434 to minimize flare in reflectivescanning mode.

The reflective original document 102 is imaged at scan line 113 alongscan line axis 114 through transparent layer 914 and through anelongated opening 1420 in the top of scan carriage 220. The opening 1420is the aperture which defines the object area actually imaged on thesensor corresponding to a given scan line. The elongated opening 1418 inthe illumination module 1420 is substantially coincident with butsubstantially wider than the opening 1420, to assure that criticalalignment of the scan line axis 114 is determined by the scan carriage220 and not by minor variations in the positioning of theremovably-disposed illumination module 1410.

Original Document Handling

As has been stated previously, an object of the invention is the abilityto change easily from reflective to transmissive scanning modes, andvice versa. Accordingly, the embodiments of the invention describedherein and illustrated in the following drawings are directed to the useof the one essential pre-scan procedure in any scanning operation: thepreparation and handling of original documents, as a means for switchingscanning modes.

In these embodiments, an original document to be scanned in reflectivescanning is placed face down on a transparent surface, as has beendescribed above. Aids to alignment of reflective media are provided, tobe described later in this specification. Transparencies are preparedoutside of the scanner using a transmissive media holder, hereinafterreferred to as a "Tx slide holder", which assures rectilinear alignmentof the original document within the holder, and proper registration ofthe surface to be scanned when the holder is placed within the scannerunit. Since the Tx slide holder can be supported accurately within thescanner, the use of one or more glass surfaces for support andregistration of a transparent original document is unnecessary. As aresult, image artifacts due to flare, Newton's rings and surfacecontamination are eliminated, along with extra time in original documentpreparation needed to overcome these problems.

Insertion of the Tx slide holder into the scanner can be used toactivate the mechanical, optical, and electronic changes accompanyingthe mode change from reflective scanning mode to transmissive scanningmode, and removal of the Tx slide holder restores those of thereflective mode. Embodiments which carry out these functions involvechanges to the illumination system 222 of FIG. 2A, or one or morecomponents of the optical system 224 detailed in the preceding sections.

FIG. 15A, FIG. 15B and FIG. 15C illustrate the use of a Tx slide holderto change the illumination mode. In this example, the three-lampremovable cartridge of FIG. 14 is movably disposed within the scancarriage, so as to position either the single transmissive-mode lamp orthe pair of reflective-mode lamps in correct alignment with the opticalsystem depending upon whether the Tx slide holder is inserted or not,respectively.

In FIG. 15A, a Tx slide holder 1510 including transparent originaldocument 1512 is inserted through an opening 1514 in the case of scanner100, and moved by motion 1516 (manually and/or automatically) intoposition using guides (not shown) substantially parallel to Tx objectfocal plane 220. Scan carriage 220 having optic axis 230 is shown in aninitial position with movably disposed illumination module 1410 inreflective scan illumination mode, i.e., with illumination axis 920aligned with optic axis 230. In the example, the module 1410 is held inposition by a magnet 1518. As the Tx slide holder 1510 is moved, a ballplunger 1520 engages surface 1522 of module 1410, pushing it into theposition shown in FIG. 15B, wherein illumination axis 924 is alignedwith optic axis 230 and module 1410 is held in position by magnet 1524.At the end of the insertion motion 1516 of Tx slide holder 1510, theball plunger 1520 engages an indent in end dock 1526, firmly seating Txslide holder 1510 and holding transparent original document 1512 inproper registration and alignment for scanning.

During a scan operation, scan carriage 220 is moved from initialposition 239 to end of scan position 240, thereby moving optic axis 230to position 242 along path 238, so as to scan original document 1512from one end to the other. After scanning, the scan carriage 220 isreturned to its initial position 239 with no change in relative positionof illumination module 1410. In FIG. 15C, Tx slide holder 1510 isremoved, reversing the insertion process by motion 1530 of the holder1510. Again, ball plunger 1520 engages illumination module 1410, thistime along surface 1532, thereby moving module 1410 to reflective modeposition with illumination axis 920 aligned with optic axis 230, andwith module 1410 again held in place by magnet 1518.

In FIG. 16A, FIG. 16B and FIG. 16C, the illumination system remainsfixed, and the insertion of the Tx slide holder causes reconfigurationof the optical system for transmissive scanning mode. FIG. 16A shows ascan carriage 220 with the optical system configured for reflectivescanning. Fixed illumination module 1410 provides illumination alongillumination axis 920 permitting scanning of original document 102placed original side down at Rx object focal plane 106. Lens 1610 isused with fixed mirror pair 1612 and movable mirror 1614 to image scanline 113 on sensor array 1616. Movable mirror 1614 is held in positionby magnet 1620.

Insertion of Tx slide holder 1510 through opening 1514 in the case ofscanner 100 moves holder 1510 with transparent original document 1512into position by motion 1516 as in the previous example. Ball plunger1520 engages surface 1622 of movable mirror 1614 moving it into positionfor transmissive mode scanning as shown in FIG. 16B, wherein it is heldin position by magnet 1624. As in the previous example, the Tx slideholder 1510 is firmly seated in end dock 1526 using ball plunger 1520.En this configuration, a scan line 113 of transparent original document1512 is illuminated along transmissive illumination axis 924, and imagedby lens 1610 on sensor array 1616. Scanning of the original document1512 is completed as scan carriage 220 is moved from initial position239 to end of scan position 240 moving optic axis 230 to position 242 bymotion 238. The end of scan position is shown in FIG. 16C.

As in the previous example, removal of the Tx slide holder 1510 reversesthe sequence of FIG. 16A, with ball plunger 1520 engaging surface 1626of movable mirror 1616 and restoring it to the correct position forreflective scanning.

The examples shown above illustrate specific examples of mode-changeoperations actuated by insertion or removal of a Tx slide holder. Itwill be apparent to one skilled in the art that many variations existfor reconfiguration of illumination and optical components, singly or incombination.

Sealed Scan Carriage

The ability to protect the optical system of a scanner by enclosing itphysically and optically has a major effect upon data quality andmaintenance requirements. As has been discussed previously, dustsettling upon optical surfaces such as mirrors, lenses or CCD arrayelements can provide contamination of the digitized signal as well asloss of sensitivity. Typical artifacts in the data include streakingalong the scanning axis. Embodiments which minimize these effects havebeen described, for example in FIG. 5A and FIG. 5B wherein upward-facingmirror elements are kept at sufficient distance from an object focalplane to avoid imaging dust particles. Other provisions, such asvertically disposed lens and CCD surfaces as shown in FIG. 8, arehelpful in minimizing dust settling effects, but cannot entirelyeliminate them as long as air movement exists within the scan carriage.

A second problem occurs as a result of light which is scattered fromoptical and other surfaces within the scan carriage, raising thebackground noise level in the captured data and introducing unwantedartifacts in the digitized image. This "flare" arises from ambient lightwhich enters the scan carriage as well as from light coming from theillumination system by other than the path of a correctly imaged objectpoint. Flare is minimized but not eliminated in the embodiments of theoptical system described previously, by reducing the number of mediumtransitions within the optical path, e.g., glass windows within whichmultiple reflections can occur, use of optical anti-reflection coatingfor lenses and CCD window glass, etc.

A third problem occurs during dark current calibration of the CCD sensorsystem, as a result of stray light entering the system from ambientsources. Since the major source of such light is from the scannerillumination system, this problem can be minimized by shutting the lampsoff during the calibration procedure. Cycling the lamps off and on againcauses stress on the lamps, thereby shortening their lifetime, andrequires a stabilization period before resumption of scanning operationsin order to avoid image quality degradation. The combined effect of thisand the previously described problems is reduction in overallproductivity of the scanning system.

The above problems are addressed in the invention by enclosing theoptical system components of the movable scan carriage in a light-sealedenclosure, protected by a "dark slide" movably disposed relative to thescan carriage such that there are no physical or optical openings in theenclosure except during an actual scan. Accordingly, there is minimalmovement of air and reduced exposure of surfaces to dust duringshipping, idle times, when originals are inserted into the scanner, andwhen the unit is opened for service. The dark slide also eliminatesnoise in the CCD signal due to ambient stray light, without thenecessity of cycling the lamps off and on during dark currentcalibration.

FIG. 17A and FIG. 17B illustrate the use of a stationary dark slidewhich seals the optical enclosure when the scan carriage is idle or indark current calibration mode. In FIG. 17A, the movable scan carriage220 of FIG. 2A is shown in reflective scanning mode, with illuminationsystem 222 illuminating scan line 113 of a reflective original document106, imaged by optical system 224 containing lens 228 on sensor system226 containing sensor array 234. The scan carriage 220 is physically andoptically sealed by enclosure 1710 except at an aperture 1712 of widthsufficient to capture fully the illuminated scan line 113. A stationarydark slide 1714 is fixed to the case of scanner 100 so as to be clear ofthe opening 1712 during scanning. In FIG. 17B, the scan carriage 220 hasbeen moved to the home position for dust protection or dark currentcalibration. In this position, the stationary dark slide 1714 completelycovers opening 1712 in sealed enclosure 1710, thereby excluding dust andlight.

An alternative to the stationary dark slide of FIG. 17A and FIG. 17B isan aperture shutter comprised of a plurality of dark slides movablyfixed to and moving with the scan carnage, as shown in FIG. 18A, FIG.18B and FIG. 18C. This embodiment provides not only for sealing theenclosure completely when idle or in dark current calibration mode, butalso for changes in aperture width and/or length according to scanningmode, thereby minimizing flare effects during scanning.

In FIG. 18A, the system is being used in reflective scanning mode. Scancarriage 220 is fitted with a sealed enclosure 1710 having fixedaperture 1712 as in the previous example. The scan carriage 220 isadditionally fitted with a pair of movably disposed slides 1810 and1812, forming a shutter which can be operated by a motor and/or otherlinkages as appropriate. In reflective scanning mode, the shutter isopened to the maximum extent, providing an opening substantially equalto the aperture 1712 of the enclosure 1710.

FIG. 18B shows the same system configured for transmissive scanningmode. In this case, the movably disposed slides 1810 and 1812 are movedcloser together, providing an opening substantially equal to thatdefining a scan line 113 at the Tx object focal plane 210. Since theshutter aperture is reduced to the minimum size used for transmissivescanning mode, flare is minimized, along with dust entry.

In the idle/dark current calibration mode, shown in FIG. 18C, the pairof slides 1810 and 1812 are moved together, thereby closing the shuttercompletely and sealing the enclosure 1710 against light and dust. Ofcourse, it should be noted that the slides 1810 and 1812 and/or otherslide configurations may also be utilized to adjustably define the widthof the scan line without departing from the scope of the presentinvention.

Drive System

An important factor in the quality of a digitized representation of anoriginal scanned by a scanner system is the uniformity and precision ofthe linear drive system used for the relative motion of the scan line ofthe scanned original along the original document in the direction of thescanning axis. Small variations in the motion result in wobbling ortilting of the scan line axis, showing up as bands and streaks in thedigitized data. In the apparatus of the invention, the illuminationsystem, optical system, and sensor system are moved together as a unitwithin the movable scan carriage. Accordingly, wobbles around an axissubstantially perpendicular to the scanning axis effectively "twist" thescan line axis with respect to a scanned original, while tilting aroundan axis substantially parallel to either the scan line axis or scanningaxis can cause variations in illumination from one scan line to thenext, which appear as bands in the digitized image.

In addition to uniformity of the linear drive system, it is necessary toindex the position of the scan line with precision, using a positionencoding system accurate to a resolution element or better. Embodimentsof the invention addressing these requirements are discussed in thefollowing discussion and accompanying drawings.

FIG. 19A and FIG. 19B show top and side views of a linear drive systemoffering uniformity and positioning precision, wherein the scan carriageis carried by a flexible drive member comprised of helically-wound bandsdisposed end-to-end, and frictionally coupled to a drive motor. In thisconfiguration, scan carriage 220 is driven by motion of band 1910 undercontrol of drive motor 1920. The band 1910 is helically wound arounddrive shaft 1922 and held in tension by springs 1924. Shafts 1926 and1928 are used as direction-changing rollers. Rotary motion of shaft 1922is converted into linear motion of the band 1910, and motion of scancarriage 220 along scanning axis 1930, within limits determined by thepositions of shafts 1926 and 1928. This linear motion provides forcomplete scanning of an original document along scanning axis 1930within the limits of window 1932.

An alternate linear drive system embodiment is shown in FIG. 20A andFIG. 20B, wherein the scan carriage is supported along one or more axessubstantially coincident with the Tx object focal plane 210. Thisconfiguration provides an effective center of rotation designed tocoincide with the scan line in the object focal plane most sensitive totilting effects described above. In the drawings, scan carriage 220 issupported at three points along rails 2006 and 2008, using passiverotating shafts 2010, 2012 and a driven shaft 2014. A friction wheel2016, attached to driven shaft 2014, is driven by the drive shaft 2022of a motor 2024. As a result of this configuration, the center ofrotation due to variations in the drive speed of motor 2024 is along arotation axis 2026 which is substantially parallel to scan line axis 114and substantially coincident with the Tx object focal plane 210. Thescan carriage 220 can be driven between limits determined by thephysical dimensions of the scan carriage 220 and the enclosure of thescanner 100 to scan an original document along scanning axis 1930 withinthe limits of window 1932.

A variety of motor and encoding configurations can be used in the drivesystem of the invention, including stepper motors and torque motors withshaft or linear-position encoders. A stepper motor provides precision inposition indexing without complexity, while using a greater amount oftime for "slew" motions of the scan carriage, i.e., when returning thecarriage to home position at the end of a scan. A torque motor, on theother hand, provides for a wide range of driving rates, but requires anencoder and feedback system to ensure positional accuracy. A shaftencoder coupled to the drive motor, or a linear encoder contained on thescan carriage itself can be used for this function.

An implementation of a linear position encoder using a linear CCD array(i.e., the linear sensor array 234 shown in FIG. 2A and FIG. 2B) isillustrated in FIG. 21. In this configuration, a number of elements ofthe linear CCD array outside an active imaging area of the scan line 113are dedicated to position encoding. Transparent surface 1932 iscomprised of active imaging area 2110 and linear encoder 2112 such thatthe scanning area 2114 imaged on the linear CCD array includes an imageof a scan line 113 of an original document 102 and an image of thelinear encoder 2112 along scan line axis 114. As shown in exploded viewin FIG. 21 the linear encoder 2112 can for example be a linear 50%duty-cycle black/white pattern in 90° quadrature 2116, having a spatialfrequency enabling exact position readout to within a resolution elementof the digitized representation of a scanned original. The image of thelinear encoder 2112, once captured by the designated elements of thelinear CCD array, can be suitably decoded according to known decodingmethods to provide accurate positional information during scanning.

Automatic Reflective Media Positioning

One of the more time-consuming activities in production scanning ispositioning of media to be scanned for correct registration andalignment. Even small alignment errors can cause angular displacementwith respect to the orthogonal coordinate system defined by the scanline axis and scanning axis. These errors must be corrected by multiplescanning iterations, or later in data processing software. In eithercase, greater user interaction and loss of overall productivity are theresult. The problem is more acute for reflective original documents thanfor transparencies since the former are opaque, placed original sidedown on the transparent surface at the Rx object focal plane, andscanned at a lower resolution (and therefore more likely to introducevisible "steps" in straight lines in the digitized image resulting fromslight angular displacement). Transparencies, on the other hand, areheld in place by features of the Tx slide holder, which can beconfigured for a particular slide size and fitted with registrationaids. Finally, since transparencies can be prepared outside the scannerat a setup workstation, the scanner does not have to be idle while setuptakes place, as is the case for preparing reflective media.

FIG. 22A and FIG. 22B show top and side views of an alignment tool builtinto the scanner according to an embodiment of the invention, directlyreferencing the scan line axis and scanning axis, and visible to theuser during the preparation of reflective media for scanning. Since thealignment grid is in permanent registration with the optical coordinatesystem, visual alignment to the grid can be quickly carried out with ahigher degree of accuracy.

In the example shown, an original document 102 to be scanned inreflective scanning mode is placed original side down on transparentsurface 106 within active scanning area 1932. An alignment grid 2210 isprovided on the top surface of the scan carriage 220 in accurateregistration with scan line axis 114. The original document 102 isaligned to the alignment grid 2210 and fixed in place, using forexample, removable tape 2212. Since the scan carriage 220 can be movedto any location within the active scanning area 1932, the alignment grid2210 is available everywhere for the alignment of the original. In analternate embodiment, the grid pattern 2210 is illuminated from belowusing an illumination source 2220 such that the grid pattern 2210 isvisible through the substrate of original document 102. In this case,even with photographic prints, the original to be scanned can itself bealigned to the grid pattern 2210 rather than only the edges of theoriginal document 102.

Another embodiment of the present invention, as shown in FIGS. 23-31C,utilizes a single switch mirror 2002 for selection between the Rx and Txobject focal planes for reflective and transmissive original documents,respectively. This particular embodiment uses either a low or highresolution focusing lens, as will be further detailed below, which incombination with other mirrors enables three distinct scanning modes: 1)reflective mode, low-resolution, 2) transmissive mode, low-resolution,and 3) transmissive mode, high-resolution. Each of these modes will bediscussed separately below.

Rx-Low Resolution

In FIG. 23, a converging device 6012 containing a low-resolution lens(shown in FIGS. 31A-31C) focuses a scan line 113 in the Rx object focalplane 106 onto an image sensor or array 6014 using switch mirrors 2002,6010 and moveable mirror 6006. This configuration defines a firstoptical pathway, indicated by reference number 2004. The illuminationsystem 6016 comprises a single aperture lamp 2020 and a switch mirror2002 configured to reflect the illumination output or light emanatingfrom lamp 2020 onto the scan line 113 of a reflective original document2090 in the Rx object focal plane 106.

Lamp 2020 is a fluorescent type (warm cathode or cold cathode) and isdisposed substantially parallel to a scan line 123 in either the Rx orTx object focal plane. The interior of lamp 2020 is coated with afluorescent material except for aperture or window 2017, which extendsalong the longitudinal axis of the lamp. Lamp 2020, together with switchmirror 2002, illuminates the scan line 113 of a reflective originaldocument 2090 held in the Rx object focal plane 106 through transparentwindow aperture 2017.

In the preferred embodiment of the present invention, switch mirror2002, as particularly shown in FIG. 25A, is sufficiently large so as toextend from the Rx object focal plane 106 to the Tx object focal plane210 thereby reflecting the maximum amount of light emanating from lamp2002. Switch mirror 2002 is preferably configured in the shape of asemi-elliptical cylinder, which by definition, includes two focalpoints. One focal point having axis 2030 extending out of the page, ispositioned substantially coincident with the lamp aperture 2017, while asecond focal point having axis 2032, also extending out of the page, ispositioned coincident with scan line 113 in the Rx object focal plane106. This particular configuration reflects the maximum amount of lightemanating from lamp 2020 onto the reflective original document 2090.However, because this type of mirror can be expensive to manufacture, asemi-cylindrical shaped mirror 2002' may be used instead, as shown inFIG. 25B. Semi-cylindrical switch mirror 2002', by definition, has onefocal point having an axis 6034 extending out of the page which ispreferably positioned equidistantly from the aperture of lamp 2017 andscan line 113.

An additional advantage in using switch mirror 2002 is that the lampaperture 2017 can be reduced in size (measured perpendicular to the lamplongitudinal axis along the circumference of the lamp) in both thereflective and transmissive modes because switch mirror 2002 gathers andfocuses more light onto scan line 113 than prior art illuminationsystems which typically illuminate the scan line directly with the lamp,without the use of any mirrors. Without switch mirror 2002, the lampaperture 2017 would need to be bigger in size to reduce the possibilityof misalignment between the lamp aperture 2017 and scan line 113.Therefore, utilizing switch mirror 2002, the lamp aperture 2017 can bereduced in size which increases the brightness of the resultingaperture. It is advantageous to increase the brightness of the lightpassing through lamp aperture 2017 to reduce exposure time of each scanline 113, resulting in an overall increase in efficiency of the system.

Illumination system 6016 may also comprise a reflecting mirror 2034having a longitudinal axis extending out of the page (not shown) andpositioned substantially parallel to lamp 2020, as shown in FIG. 24.Mirror 2034, if present, is configured to illuminate scan line 113 inthe Rx object focal plane 106 from the opposite side of optical pathway2004 as light reflected by switch mirror 2002. In the preferredembodiment of the present invention, mirror 2034 reflects excess lightgenerated by lamp 2020 (i.e., ambient light not passing through aperture2017). However, a second aperture (not shown) of lamp 2020 may be usedto illuminate scan line 113 via mirror 2034. It is preferable to usemirror 2034 together with switch mirror 2002 for illuminating scan line113 more uniformly thereby providing better balancing of the light onthe reflective original document 2090 and hence, a better scan.

Returning to FIG. 23, moveable mirror 6006 is tilted at angle .0. todirect optical pathway 2004 onto switch mirror 6010, angle .0. beingmeasured between the substantially vertical optical pathway 2004 andoptical pathway 6008, which is defined by the optical pathway frommoveable mirror 6006 to switch mirror 6010. In the preferred embodimentof the present invention, angle .0. is approximately 15°.

Tx-Low Resolution

FIG. 26 illustrates the rotation of switch mirror 2002 for illuminatinga transmissive original document 2091 held by a Tx slide holder 2042 inthe Tx object focal plane 210. Switch mirror 2002 pivots around axis2048 in the direction of arrow 2040, this movement being effectuated byinsertion of the Tx slide holder 2042 in the direction of arrow 2095(either manually and/or automatically) into position using guides (notshown) substantially parallel to the Tx object focal plane 210. If theoperator desires to scan a reflective original document 2090, switchmirror 2002 may be returned to the reflective position (shown in FIG.23) by means of a conventional solenoid (not shown) or other suitablemeans. As shown more particularly in FIG. 28, when switch mirror 2002 ispositioned to reflect light onto the transmissive original document 2091in the Tx object focal plane 210, it has the immediate advantage ofreflecting light at an acute angle (shown by light paths 2052) so anyscratches in the transmissive original document will be minimized in thesubsequent digitized recording. Additionally, lamp aperture 2017 can bereduced in size because switch mirror 2002 gathers and focuses a greateramount of light than prior art illumination systems, as described above,which results in an increased efficiency in the scanning system.

FIG. 27 illustrates the scanning of a transmissive original document2090 held in the Tx object focal plane at low resolution using the samefocusing lens in converging device 6012 as the reflective mode,low-resolution scanning system of FIG. 23. It should be noted that thecorresponding second optical pathway 2050 is separated by a distance Xfrom the first optical pathway 2004 which, as described above,corresponds to scanning reflective original documents 2090. Accordingly,moveable mirror 6006 must be moved to direct optical pathway 2050 ontoswitch mirror 6010. Movement of mirror 6006 may be effectuated by a leadscrew rotated by a conventional solenoid (not shown) or other suitablemeans. It is important that the total optical pathway length remainconstant so that the transmissive original document 2091 is projectedonto sensor array 6014 with the same magnification as the reflectiveoriginal document 2090. Therefore, moveable mirror 6006 is moveddownward a distance Y and over a distance X to compensate for distanceD, where D is the separation distance between the Rx object focal plane106 and Tx object focal plane 210. Using simple trigonometry, theequation:

    D=Y+Z                                                      [3]

is easily derived. Similarly, the equations

    D=Y(1+1/COS.0.)                                            [4]

    X=Y(TAN.0.)                                                [5]

can also be derived. Thus, by knowing equations 4 and 5, moveable mirror6006 is positioned to compensate for the separation distance D so thatthe total optical pathway length remains constant.

Tx-High Resolution

FIG. 29 illustrates rotation of switch mirror 6010 for scanning atransmissive original document 2091 at high resolution. Convergingdevice 6012, as will be described below, simultaneously selects a highresolution lens. Switch mirror 6010 rotates about pivot axis 2060 andmay be rotated by a conventional solenoid (not shown) or other suitablemeans. 20 This configuration defines a third optical pathway 3040, whereswitch mirror 6010 reflects a scan line 113 of the transmissive originaldocument 2091 through converging device 6012 onto sensor array 6014.This configuration has the immediate advantage of eliminating a mirrorfrom the optical pathway 3040 (i.e., moveable mirror 6006) whichincreases quality in which the original document is scanned, asdescribed above.

Although three distinct optical configurations have been illustratedabove, other configurations are possible, for example, as shown in FIG.30. In this embodiment, moveable mirror 2006 directs optical pathway5002 corresponding to scan line 113 from either reflective ortransmissive object focal plane 106, 210 directly onto the sensor array6014 through the converging device 6012. Of course, moveable mirror 6006would need to move, as described above, depending on whether theoriginal document was in the reflective or transmissive object focalplane 106, 210 so the total optical pathway would thereby remainconstant. However, it should be noted that more space inside theflat-bed scanner is required for this particular embodiment.

FIGS. 31A-31C illustrate switching a low resolution lens 3002, which isused in scanning both reflective and transmissive original documents2090, 2091, to a high resolution lens 3004, for scanning onlytransmissive original documents. It is preferable to use two separatelenses with a predetermined focal length and magnification because theyare less expensive than single zoom lens configurations. Lenses 3002 and3004 are mounted on a lens carriage 3010 which is slideably mounted (indirection of double headed arrow 3070) on a mounting carriage 3041. Themounting carriage 3041, in turn, is slideably movable relative to scancarriage 220 (in the direction of double headed arrow 3071) by beingengaged and guided by rail 3046 and threadedly engaged and driven bylead screw 3044.

FIG. 31C further details the lens carriage 3010. A slot or groove 3052is shown which extends diagonally across lens carriage 3010. A pin 3050,which may include a roller bearing, is fixedly mounted to scan carriage220 directly underneath optical pathway 4002 and extends into groove3050. In operation, drive motor 3042 causes lead screw 3044 to rotatecausing mounting carriage 3041 to slide relative to scan carriage 220,parallel to optical pathway 4002. Simultaneously, the fixed pin 3050forces the lens carriage 3010 to slide relative to mounting carriage3041, in the direction of arrow 3070. In this manner, drive motor 3042,in response to a controller (not shown), causes low-resolution 3002 orhigh-resolution 3004 lens to move into optical pathway 4002. Asdescribed above, typically the low-resolution lens 3002 is used forscanning original documents in the reflective and transmissive modewhile a higher-resolution lens 3004 may be used in the transmissivemode.

Another feature of the groove 3052 is that the ends thereof 3054 aresubstantially parallel to optical pathway 4002. Thus, when either lens3002, 3004 is selected to be in the optical pathway 4002, a respectiveend 3054 of groove 3052 will be positioned proximate the fixed pin 3050.Thus, after fixed pin 3050 and groove 3052 work conjunctively to slidelens carriage 3010 so that either lens is positioned in optical pathway4002, the fixed pin 3050 is now positioned in the end of groove 3054.This configuration allows movement of the lens carriage 3010 along adirection substantially parallel to optical pathway 4002. Accordingly,the same drive motor 3042 can be used to switch lenses 3002, 3004 andautomatically focus the image of the transmissive or reflective originaldocument by moving lens carriage 3010 closer to or further from thesensor focal plane 3015 in response to an algorithm executed by acomputer. The sensor array 6014 typically can identify up to 256 levelsof color for each pixel. The algorithm finds a high-contrast area ofadjacent pixels (i.e., where there is a crisp transition from dark tolight or vice versa) of the reflective original image and reiterativelymaximizes the difference of the numeric value represented by the pixelsby moving a respective lens closer to or further from the sensor focalplane 3015.

The foregoing description of the present invention has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed, andobviously many modifications and variations are possible in light of theabove teaching. Such modifications and variations that may be apparentto a person skilled in the art are intended to be included within thescope of this invention as defined by the accompanying claims.

What I claim and desire to secure by Letters of Patent of the UnitedStates are the following:
 1. A flat-bed scanner for scanning an originaldocument to obtain a digitized representation of said original document,said flat-bed scanner comprising:a stationary reflective object focalplane for supporting a reflective original document; a stationarytransmissive object focal plane disposed substantially parallel to andat a vertical distance below said stationary reflective object focalplane, for supporting a transmissive original document; a scan carriagemovably disposed for linear motion along a scanning axis; and anillumination system for illuminating a scan line of said originaldocument in said reflective or transmissive object focal plane, saidscan line being substantially perpendicular to said scanning axis, saidillumination system being enclosed within said scan carriage andcomprising an illumination source having a single lamp, said lampdisposed along a lamp axis substantially parallel to said scan line ofsaid original document, said illumination system further comprising asingle switch mirror for selectively redirecting an illumination outputof said lamp to illuminate said scan line in said reflective ortransmissive object focal plane.
 2. A flat-bed scanner according toclaim 1, wherein said illumination system further comprises a reflectingmirror configured to redirect said illumination output of said lamp toilluminate said scan line in said reflective object focal plane.
 3. Aflat-bed scanner according to claim 2, wherein said output illuminationredirected from said reflecting mirror impinges upon said scan line insaid reflective object focal plane at a different angle than said outputillumination redirected from said switch mirror.
 4. A flat-bed scanneraccording to claim 1, wherein said lamp has an elongated transparentaperture window parallel to said lamp axis, and wherein saidillumination source illuminates said scan line in said reflective ortransmissive object focal plane through said transparent windowaperture.
 5. A flat-bed scanner according to claim 1, wherein saidstationary transmissive object focal plane includes a holder forsupporting said transmissive original document, said holder beingslideably moveable in a direction substantially parallel to saidscanning axis for causing said switch mirror to redirect saidillumination output onto said scan line in said transmissive objectfocal plane.
 6. A flat-bed scanner according to claim 1, furthercomprising optical means, enclosed within said scan carriage, forobtaining a digitized representation of said scan line.
 7. A flat-bedscanner according to claim 1, further comprising means for moving saidscan carriage along said scanning axis to obtain digitizedrepresentations of successive scan lines of said original document insaid reflective or transmissive focal plane, said digitizedrepresentations of said successive scan lines together comprising saiddigital representation of said original document.
 8. A flat-bed scanneraccording to claim 6, wherein said optical means further comprises:animage sensor disposed within said scan carriage; a first reflectingmirror for reflecting said illumination output onto said image sensor,said first reflecting mirror being moveable and having a first positionfor reflecting illumination output reflected by said reflective originaldocument and a second position for reflecting illumination outputpassing through said transmissive original document; and convergingmeans disposed between said first reflecting mirror and said imagesensor for converging said scan line onto said image sensor.
 9. Aflat-bed scanner according to claim 6, further comprising:an imagesensor disposed within said scan carriage; a first reflecting mirrorbeing moveable and having a first position for reflecting illuminationoutput reflected by said reflective original document and a secondposition for reflecting illumination output passing through saidtransmissive original document; a second reflecting mirror configured toreflect said illumination output reflected by said first reflectingmirror onto said image sensor; and converging means disposed betweensaid second reflecting mirror and said image sensor for converging saidscan line onto said image sensor.
 10. A flat-bed scanner according toclaim 6, wherein said optical means further comprises:an image sensordisposed within said scan carriage; a reflecting mirror configured toreflect illumination output passing through said transmissive originaldocument onto said image sensor; and converging means disposed betweensaid reflecting mirror and said image sensor for converging said scanline onto said image sensor.
 11. The flat-bed scanner according to claim6, wherein said optical means further comprises:an image sensor disposedwithin said scan carriage; a first optical pathway having a firstreflecting mirror being configured to reflect illumination outputreflected by said reflective original document, said first opticalpathway further including a second reflecting mirror configured toreflect said illumination output reflected by said first reflectingmirror onto said image sensor; a second optical pathway including saidfirst and said second reflecting mirrors, wherein said first reflectingmirror is further configured to reflect illumination output passingthrough said transmissive original document; a third optical pathwayincluding said second reflecting mirror configured to reflectillumination output passing through said transmissive original documentonto said image sensor; and converging means disposed between saidsecond reflecting mirror and said image sensor for converging said scanline onto said image sensor.
 12. The flat-bed scanner according to claim1, wherein said lamp is a cold cathode fluorescent lamp.
 13. Theflat-bed scanner according to claim 1, wherein said lamp is a warmcathode fluorescent lamp.
 14. The flat-bed scanner according to claims8, 9, 10, or 11, wherein said converging means includes a first and asecond optical lens.
 15. The flat-bed scanner according to claim 14,wherein said first lens is a lower resolution lens than said secondlens.
 16. The flat-bed scanner according to claim 15, further comprisinga drive device for moving said first or said second optical lens into anoptical pathway corresponding to said reflective or transmissive objectfocal plane.
 17. The flat-bed scanner according to claim 16, whereinsaid drive device moves said first and second lens closer to or furtherfrom said image sensor for automatically focusing said original documentonto said image sensor.
 18. The flat-bed scanner according to claim 1,wherein said switch mirror rotates about a longitudinal axis thereof,said longitudinal axis being aligned substantially parallel to said scanline of said original document, said switch mirror having at least twopositions for redirecting said illumination output to either saidreflective or said transmissive object focal plane.
 19. The flat-bedscanner according to claim 18, wherein said switch mirror is configuredin the shape of an semi-elliptical cylinder.
 20. The flat-bed scanneraccording to claim 18, wherein said switch mirror is configured in theshape of a semi-cylinder.